The Kilo Class (Project 877) submarine was designed for anti-submarine and anti-ship warfare in the protection of naval bases, coastal installations and sea lanes, and also for general reconnaissance and patrol missions. The Kilo is considered to be to be one of the quietest diesel submarines in the world. The submarine consists of six watertight compartments separated by transverse bulkheads in a pressurised double-hull. This design and the submarine's good reserve buoyancy lead to increased survivability if the submarine is holed, even with one compartment and two adjacent ballast tanks flooded. The foreplanes are positioned on the upper hull in front of the fin or sail. The command and control systems and fire control systems are located in the main control room which is sealed off from the other compartments.

The Project 636 design is a generally improved development of the Project 877EKM Kilo class that represents an interim design between the standard 'Kilo' and the new Lada project. The Project 636 is actively promoted for the world market by the Rosvoorouzhenie state-owned company. This submarine has improved range, firepower, acoustic characteristics and reliability. Visually distinguished by a step on the aft casing, the length of the hull is extended by two frame spacings (2 x 600 mm). The additional length permitted increasing the power of diesel-generators and mounting them on improved shock-absorbing support, and reducing twofold the main propulsion shaft speed. Owing to these improvements, the submarine speed and sea endurance were increased, while the noise level was radically decreased. The low noise level of the submarine has been achieved with the selection of quiet machinery, vibration and noise isolation and a special anti-acoustic rubber coating applied on the outer hull surface.

The Project 636 is equipped with six 533 mm forward torpedo tubes situated in the nose of the submarine and carries eighteen torpedoes with six in the torpedo tubes and twelve stored on the racks.
Alternatively the torpedo tubes can deploy mines. The submarine can carry 24 mines with two in each of the six tubes and twelve on the racks. Two torpedo tubes are designed for firing remote-controlled torpedoes with a very high accuracy. All torpedo tubes and their service systems provide effective firing from periscope to operational depths. The computer-controlled torpedo system is provided with a quick-loading device. It takes only 15 seconds to prepare stand-by torpedo tubes for firing: The first salvo is fired within two minutes and the second within five minutes.

The Russian fleet operates three variants of the Kilo 877: the basic 877; the 877K that has an improved fire-control system; and the 877M that has wire-guided torpedoes from two tubes. Export models, designated with an 'E' suffix, are generally similar though with some reduced features. A total of at least 26 and perhaps as many as 30 were built for the Russian navy, one of which was subequently exported to Iran. All the 30 Kilo-class submarines built for service with the Russian Navy are designated Project 877, although 15 of these are the earlier-developed 877EKM and 15 the later 636 versions. As of early 2000 as many as 14 units were believed to remain active, with an additional 7 in reserve, though specific identities are not known.

As of early 1998 construction of the Project 877EKM submarines was nearly completed, with only one submarine left under construction in St.Petersburg for the Indian Navy. Russia exported 21 Project 877 and 636 submarines, including: India - 10, and China - 4, Iran - 3, Algeria - 2, Poland - 1, Romania - 1.

On 04 August 1993, Iran took delivery of a second Russian Kilo-class diesel submarine, and the third
arrived 18 January 1996. Russia went ahead with the first two deliveries despite vigorous US protests. In response to Administration pressure and US sanctions legislation, Russia formally pledged in June 1995 not to enter any new arms contracts with Iran, although prior arms contracts could be implemented.

India took delivery of the first of the two additional Russian-built Kilo class submarines in January 1999. On 17 August 2000 the Sindhushastra began the two month voyage from St Petersburg to India. The 877EKM submarine was the last in a series of 10 submarines built at Russian shipyards for Indian customers. In August 2000 the Zvezdochka engineering enterprise at Severodvinsk started the work of servicing and modernizing the Indian series-877EKM submarine Sinduratna, the second Indian sub to have had a refit at Zvezdochka. In 1999 the Indian Navy took delivery of the Sinduvir, the first submarine to have been modernized at Severodvinsk. The Sinduratna will be the second Indian submarine to be fitted with four ZM-54E1 missiles, with a range of 300 km. The missiles are part of the latest Klab-S anti-ship missile complex designed by the Novator bureau at Yekaterinburg.

In the spring of 1997, the first Project 636 submarine was launched, and China became the first customer for this submarine. The last of four export Kilo-class boats for China, the second improved model Project 636 unit, was launched on 17 June 1998 and departed the Baltic aboard a heavy-lift ship on 11 December 1998, bound for the submarine base at Ning-bo. China is also said to be interested in purchasing several more 636 series submarines, one of which is now in an unfinished state at the Krasnoye Sormovo yard in Nizhniy Novgorod, while others may be built at the Admiralteyskiye Verfi [Admiralty Shipyards] in St Petersburg.